It has been proposed to use stimulation of the heart chambers to control disorders of myocardial contraction observed in patients with heart failure, whether the disorders were spontaneous or induced by traditional stimulation. This therapy has often observed dramatic positive results for patients with heart failure whose condition was not improved with conventional treatments.
This therapy is designed to resynchronize the contraction of the heart chambers (atrium and ventricle, and both ventricles) in order to improve the patient by optimizing the different phases of the hemodynamics cycle, this cycle including: pre-ejection, isovolumetric contraction, systolic ejection, isovolumetric relaxation, and finally filling of the cavity.
Most of these known devices implement a technique called cardiac resynchronization therapy (“CRT”) or bi-ventricular pacing (“BVP”), delivering as needed electrical pulses to ensure a joint and permanent stimulation of the left and right ventricles to resynchronize them. For this purpose a device with electrodes to stimulate both ventricles is implanted in a patient, the device applying between the respective moments of stimulation of the left and right ventricles a delay, called “interventricular delay.” The interventricular delay can be adjusted to resynchronize the contraction of both ventricles with fine optimization of the patient's hemodynamic status. Such a CRT pacemaker is, for example, disclosed in EP 1108446 A1 and its counterpart U.S. Pat. No. 6,556,866 (both assigned to Sorin CRM S.A.S., of Clamart, France, previously known as ELA Medical, of Montrouge, France), which is incorporated herein by return in its entirety.
This technique of biventricular resynchronization only addresses, however, the form of heart failure known as “systolic failure.” In this form of the disease, the heart muscle is unable to provide the force necessary to ensure adequate cardiac output, and the patient shows signs of dilatation, leading to a lengthening of the QRS complex, which is the expression of delayed left ventricular depolarization, resulting in desynchronization. A CRT/BVP device can then resynchronize the ventricles and make the cardiac contraction more uniform.
There is another form of heart failure, known as “diastolic failure,” which is a failure with “preserved systolic function” and has no characteristic of desynchronization of the ventricles. Rather, it comes from a lack of or incomplete left ventricular filling.
A CRT/BVP therapy is of no effect in this case. However, the diastolic failure form of the disease affects nearly 40% of heart failure patients, and there is no known effective treatment to address it.
The starting point of the present invention is the recognition by the inventor that this clinical form of disease may particularly be the result of a conduction disorder in the atria (interatrial block), which delays the depolarization, and therefore the contraction, of the left atrium from the right atrium. However, as the atrio-ventricular conduction paths otherwise behave normally, the depolarization and contraction of both ventricles occurs within a reasonable time, and with no desynchronization between the ventricles. Therefore, the interatrial block introduces a poor synchronization between the contraction of the left atrium and the left ventricle: the delay of the contraction of the left atrium is such that it contracts almost simultaneously with the left ventricle, and therefore can not properly fullfil its function to finish the filling of the left ventricle.
The U.S. Patent Publication No. 2005/0102002 A1 describes a device equipped with a sensor measuring a hemodynamic parameter (intra-ventricular pressure sensor, pulmonary venous flow sensor, flow sensor through the mitral valve, acoustic sensor, and accelerometer) the signal of which is used to calculate a representative index of the diastolic function of the patient. The stimulation parameters are modified as necessary to maximize the performance index, for example, by appropriate selection of the stimulation sites and/or control of the atrio-ventricular delay.
The U.S. Patent Publication No. 2007/0179542 A1 describes another device of the same type, including a sensor delivering an LV acceleration signal representative of the contraction of the left ventricle. The device also comprises means for varying the atrioventricular (AV) and interatrial (AA) delays based on various parameters, including the LV acceleration signal of the left ventricle, to try to improve the patient's cardiac function. This document provides in particular to adjust iteratively the AV delay based on the LV acceleration signal measured, until an optimal sequencing value between the contractions of the atrium and those of the ventricle is found.
Other techniques have been proposed for treating diastolic heart failure, such as effecting a premature stimulation of the left atrium either by “overdrive”, a technique of stimulation of the left atrium at a frequency slightly higher than the frequency of a spontaneous sinus rhythm (i.e., the rhythm of the right atrium), or triggering the stimulation of the left atrium from the detection of the depolarization of the right atrium.
Both methods are purely electric (i.e., they are based on the detection of the depolarization signals), and their effectiveness can only be validated by a hemodynamic analysis, for example, by an echocardiographic examination. In addition, they provide no adaptation for exercise in case of a change of patient activity, or in case of possible changes in the conduction of the cardiac tissue over time.